System comprising magnetically actuated motion control device

ABSTRACT

A system that includes a magnetically actuated motion control device comprising a housing defining a cavity and including a slot therethrough. A movable member is located within the cavity and is movable relative to the housing. A magnetic field generator located on either the housing or the movable member causes the housing to press against the movable member to develop a friction force.

This application is a divisional of U.S. patent application Ser. No.10/080,293, filed Feb. 20, 2002, now U.S. Pat. No. 6,640,940 which is adivisional of U.S. patent application Ser. No. 09/537,365, filed Mar.29, 2000 (now U.S. Pat. No. 6,378,671, issued on Apr. 30, 2002).

FIELD OF THE INVENTION

The present invention relates to magnetically actuated motion controldevice. In particular the present invention relates to magneticallyactuated motion control devices that vary contact pressure between afirst member and a second member in accordance with a generated magneticfield.

BACKGROUND AND RELATED ART

Magnetically actuated motion control devices such as magneticallycontrolled dampers or struts provide motion control, e.g., damping thatis controlled by the magnitude of an applied magnetic field. Much of thework in the area of magnetically controlled dampers has focused oneither electrorheological (ER) or magnetorheological (MR) dampers. Theprinciple underlying both of these types of damping devices is thatparticular fluids change viscosity in proportion to an applied electricor magnetic field. Thus, the damping force achievable with the fluid canbe controlled by controlling the applied field. Examples of ER and MRdampers are discussed in U.S. Pat. Nos. 5,018,606 and 5,384,330,respectively.

MR fluids have high yield strengths and viscosities, and therefore arecapable of generating greater damping forces than ER fluids. Inaddition, MR fluids are activated by easily produced magnetic fieldswith simple low voltage electromagnetic coils. As a result, dampersemploying MR fluids have become preferred over ER dampers.

Because ER and MR fluid dampers still involve fluid damping, the dampersmust be manufactured with precise valving and seals. In particular, suchdampers typically require a dynamic seal and a compliant containmentmember which are not particularly easy to manufacture and assemble.Further, the fluid type dampers can have significant “off-state” forceswhich can further complicate manufacture and assembly. Off-state forcesrefer to those forces at work in the damper when the damper is notenergized.

The foregoing illustrates limitations known to exist in present devicesand methods. Thus, it is apparent that it would be advantageous toprovide an alternative directed to overcoming one or more of thelimitations set forth above. Accordingly, a suitable alternative isprovided including features more fully disclosed hereinafter.

SUMMARY OF THE DISCLOSURE

According to one aspect of the invention, a magnetically actuated motioncontrol device is provided. The magnetically actuated motion controldevice includes a housing, and movable member and a magnetic fieldgenerator located on either the housing or the movable member. Thehousing defines a cavity in which the movable member is located andincludes at least one slot. A magnetic field applied by the fieldgenerator causes the housing to press against the movable member andthereby provide friction damping.

According to another aspect of the invention, a sensor for sensing theposition of a movable member relative to a housing of a magneticallycontrolled damper is provided. The sensor includes a first membersecured to the housing, a second member, such as a slide, that iscoupled to the movable member so that the relative position of the firstmember and the second member relates the position of the movable memberwithin the housing. According to an exemplary embodiment, the movablemember can include a depression for receiving an extension on the secondmember of the sensor. The extension of the second member fits through aslot in the housing and into the depression to couple the second memberof the sensor to the movable member. In another embodiment, the secondportion of the sensor can be configured so as to be in rolling contactwith the movable member. In this embodiment, relative rotation betweenthe first member and the second member indicates relative motion betweenthe movable member and the housing.

The foregoing and other aspects will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will be understood byreading the following detailed description in conjunction with thedrawings in which:

FIG. 1 is a cutaway side sectional view of a first exemplary embodimentof the present invention.

FIG. 2 is an end sectional view taken along section 2—2 in FIG. 1.

FIG. 3A is a side view of a housing according to a second exemplaryembodiment of the present invention.

FIG. 3B is an end sectional view taken along section 3—3 in FIG. 3A.

FIG. 4A is a side view of a housing according to a third exemplaryembodiment of the present invention.

FIG. 4B is an end sectional view taken along section 4—4 in FIG. 4A.

FIG. 5A is a side view of a housing according to a fourth exemplaryembodiment of the present invention.

FIG. 5B is an end sectional view taken along section 5—5 in FIG. 5A.

FIG. 6 is a cutaway side sectional view of a fifth exemplary embodimentof the present invention.

FIG. 7 is a cutaway sectional view of a sixth exemplary embodimentaccording to the present invention.

FIG. 8 is a cutaway side sectional view of a seventh exemplaryembodiment according to the present invention.

FIG. 9 is a side cutaway sectional view of a eighth exemplary embodimentof the present invention.

FIG. 10A is a schematic diagram illustrating the magnetic field producedby permanent magnets in a damper according to the eighth exemplaryembodiment.

FIG. 10B is a schematic diagram of the magnetic field produced by coilsin a damper according to the eighth exemplary embodiment.

FIG. 10C is a schematic diagram of the magnetic field resulting from theaddition of the magnetic fields shown in FIGS. 10A and 10B.

FIG. 11 is a cutaway side sectional view of a ninth exemplary embodimentof the present invention.

FIG. 12 is a graph showing the relationship between damping force andcurrent for a damper constructed in accordance with the presentinvention.

FIG. 13 is a perspective view of a tenth exemplary embodiment of thepresent invention.

FIG. 14 is a perspective exploded view of the embodiment shown in FIG.13.

FIG. 15 is a side view of an embodiment of the present inventionincluding an outer layer of acoustically insulating material.

FIG. 16 is a cutaway side sectional view of an eleventh embodiment ofthe present invention.

FIG. 17 is an end sectional view taken along section 17—17 in FIG. 16.

FIG. 18 is an exploded perspective view of the embodiment shown in FIGS.16 and 17.

FIG. 19 is a cutaway side sectional view of a twelfth exemplaryembodiment according to the present invention.

FIG. 20 is a cutaway side sectional view of a thirteenth exemplaryembodiment according to the present invention.

FIG. 21 is a cutaway side sectional view of a fourteenth exemplaryembodiment according to the present invention.

FIG. 22 is a cutaway side sectional view of a fifteenth exemplaryembodiment according to the present invention.

FIG. 23 is an end sectional view taken along section 23—23 in FIG. 22.

FIG. 24 is a schematic illustration of a washing machine employing anembodiment of the present invention.

FIG. 25 is a schematic illustration of an embodiment of the presentinvention used in an automobile, truck, or other vehicle.

FIG. 26A is a schematic illustration of an embodiment of the presentinvention used as a damper in a chair.

FIG. 26B is a schematic illustration of an embodiment of the presentinvention being used to control the tilt of the chair shown in FIG. 26A.

FIG. 27 is a schematic illustration of a height adjustable tableemploying an embodiment of the present invention.

FIG. 28A is a schematic illustration of an embodiment of the presentinvention used for locking a tilting door.

FIG. 28B is a schematic illustration of an embodiment the presentinvention used for locking a tilting work surface.

FIG. 29 is a side schematic illustration of an embodiment of the presentinvention used as a rotary brake in a force feedback steering wheel.

FIG. 30 is a schematic side sectional illustration of a computerpointing device employing an embodiment of the present invention asrotary brakes.

FIG. 31 is a schematic side sectional illustration of an active forcefeedback steering wheel employing an embodiment of the present inventionas a brake.

FIG. 32 is a schematic illustration of a device for holding irregularobjects employing an embodiment of the present invention.

FIG. 33 is a cutaway side sectional view of a sixteenth exemplaryembodiment according to the present invention.

FIG. 34 is a cutaway side sectional view of a seventeenth exemplaryembodiment according to the present invention.

FIG. 35 is a cutaway side sectional view of a eighteenth exemplaryembodiment according to the present invention.

FIG. 36A is a schematic side sectional view of a nineteenth exemplaryembodiment according to the present invention.

FIG. 36B is a sectional view taken along section 36—36 in FIG. 36A.

FIG. 37A is a side view of the housing according to the embodiment shownin FIG. 36A.

FIG. 37B is an end view of the housing shown in FIG. 37A.

FIG. 38A is a side view of a housing according to a twentieth exemplaryembodiment according to the present invention.

FIG. 38B is an end view of the housing shown in FIG. 38A.

FIG. 39 is a side sectional view of a twenty-first exemplary embodimentof the present invention.

FIG. 39A is a partial view of the housing of FIG. 39.

FIG. 40 is a side sectional view of the embodiment shown in FIG. 39 inan on-state.

FIG. 40A is a partial view of the housing of FIG. 40.

FIG. 41A is a sectional view taken along section 41—41 in FIG. 40.

FIG. 41B is a perspective view of a spring in the embodiment shown inFIG. 41A.

FIG. 41C is a perspective view of a bearing in the embodiment shown inFIG. 41A.

FIG. 42 is a cutaway side sectional view of a twenty-second exemplaryembodiment according to the present invention.

FIG. 43 is a cutaway side sectional view of a twenty-third embodimentaccording to the present invention.

FIG. 44 is a schematic view of the embodiment shown in FIG. 39 employedin a car door.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

For a better understanding of the invention, the following detaileddescription refers to the accompanying drawings, wherein exemplaryembodiments of the present invention are illustrated and described.

The present invention relates to a magnetically actuated alternative totraditional MR fluid motion control devices. A magnetically actuatedmotion control device according to the present invention can be embodiedas linear or rotary dampers, brakes, lockable struts or position holdingdevices. The invention contains no MR fluid, yet provides a variablelevel of coulombic or friction damping that is controlled by themagnitude of the applied magnetic field.

In contrast to MR or ER fluid devices, a magnetically actuated motioncontrol device according to the present invention is simple tomanufacture and relatively low cost. A magnetically actuated motioncontrol device according to the present invention also allows for veryloose mechanical tolerances and fit between components. In addition, amagnetically actuated motion control device according to the presentinvention does not require a dynamic seal or a compliant containmentmember as does a fluid type damper, and is therefore relatively easy tomanufacture and assemble. Further, a magnetically actuated motioncontrol device according to the present invention has particularly lowoff-state forces which provide for a wide dynamic range between theoff-state and a maximum damping force.

An example of a magnetically actuated motion control device according tothe present invention includes a magnetically permeable tubular housingthat moves relative to an electromagnetic piston and includes one ormore coils, an associated magnetically permeable core or core pieces andassociated pole regions. Although the housing in this example istubular, a housing can be of any suitable cross section, including, butnot limited to a rectangular cross section. The pole regions are locatednear an interface between the piston and the housing and carry magneticflux in a generally radial direction with respect to a longitudinal axisrunning along the housing. The housing includes at least one slot buttypically includes an array of slots. The housing slots allow thehousing to flex and constrict radially when a magnetic field is appliedby directing current through the coils. In so doing, the inner surfaceof the housing squeezes against the outer surface of the piston with anormal force that is approximately proportional to the magnitude of theapplied magnetic field. Thus, the housing acts like a magneticallyactuated collet that squeezes the piston to resist relative movementbetween the housing and the piston. Generally, the magnitude of theapplied magnetic field is proportional to the electric current suppliedto the coil. The damping force thus depends on the coefficient offriction between the inner surface of the housing and the outer surfaceof the piston and the normal force between these surfaces, which isdependent on the magnetic field produced by running current through thecoils.

The invention allows for the accommodation of very loose mechanicaltolerances or fit between the housing and the piston. Because thepresent invention does not require a dynamic seal or compliantcontainment member, it offers particularly low off-state forces and issimple to manufacture and assemble.

The present invention is particularly suitable for making low-cost,high-volume linear dampers for use in household appliances such aswashing machines. Other applications for magnetically actuated motioncontrol devices according to the present invention include simple rotaryor linear brakes for controlling mechanical motions inside officeequipment such as copiers or printers, e.g., paper feed mechanisms.Additional applications for magnetically actuated motion control devicesaccording to the present invention include dampers for use assemi-active control elements in conjunction with ultra-low vibrationtables and platforms. Magnetically actuated motion control devicesaccording to the present invention can also be used as latching orlocking mechanisms in office furniture, e.g., props and latches fordoors, drawers, etc. Still other applications include exerciseequipment, rehabilitation equipment, joysticks, seismic structuralcontrol dampers, avionics semi-active control devices, machine toolfixturing devices, ventilation system flaps and doors in automobiles,and sliding doors in vehicles, etc.

Magnetically actuated motion control devices according to the presentinvention can also be used in the area of haptics. The field of hapticsincludes devices used in computer peripherals such as force-feedbacksteering wheels, programable detents, computer pointing devices andjoysticks used with games and other software. This field also includesindustrial force feedback mechanisms such as steering wheels onsteer-by-wire vehicles.

Yet another application is to use either linear or rotary embodiments ofthe invention in conjunction with pneumatic and hydraulic actuators toenable precision position and velocity control.

Turning to the drawings, a first exemplary embodiment of a magneticallyactuated motion control device according to the present invention isshown in FIGS. 1 and 2. The first embodiment motion control device is adamper 101 and includes a housing 103 defining a cavity 105 in which apiston 107 is located. The housing 103 includes a least one longitudinalslot 109 (five of eight such slots can be seen in FIG. 1). The housingshown in FIG. 1 includes a plurality of slots that pass through thehousing wall to define flexible bands, tabs, or fingers 111. The slots109 extend through the wall of the housing 103 and extend nearly theentire length of the housing 103. Although narrow slots are illustratedin the Figures, it should be understood that a suitable wide slot couldalso be provided in the housing.

The piston 107 includes a shaft 112 having a magnetically active portion113 made up of at least one, and preferably two electromagnetic coils115 set in a magnetically permeable core 117. Although here themagnetically permeable core 117 is hollow, the core can alternatively bea solid bobbin. A hollow core allows space for connecting wires or foran axial screw or rivet. However, a solid core is preferable becausemagnetic saturation of the core is reduced.

In addition, the core can be made up of a plurality of core pieces. Acurrent source 118 supplies current to the coils 115 through wires 119.Each end of the damper preferably includes a structure which facilitatesattaching damper 101 to other structures, such as clevis eye 121 forattaching the end to a portion of a damped component.

Current flowing through the coils 115 creates a magnetic field thatdraws the housing 103 in toward the piston 107. For this purpose, thehousing 103 is formed of a material which will be attracted by themagnetic field. Examples include, but are not limited to, steels andother iron alloys. The amount of current flowing through the coils 115is generally directly proportional to the magnitude of the magneticfield generated. Thus, control of the electric current flowing throughthe coils 115 can be used to control the normal or pressing forcebetween the inner surface of the housing 103 and the outer surface ofthe piston 107, thereby controlling the damping effect of the damper101.

An illustration of the damping effect can be seen in the end sectionalview shown in FIG. 2, which shows the relationship of the slottedhousing 103 with respect to the piston 107. When no magnetic field isapplied, the piston 107, and particularly the active portion 113, fitsloosely within the housing 103 to define a small radial clearance 123between the housing 103 and the magnetically active portion 113 of thepiston 107. That is, the housing 103 is relaxed and does not pressagainst the piston 107. When current is supplied to the coils 115 themagnetic field generated causes the flexible fingers 111 in the housing103 to be attracted radially inward as indicated by the arrows 125 suchthat the housing 103 squeezes the piston 107 with a force proportionalto the applied magnetic field, and therefore the applied current.

The slotted housing 103 and the core 117 of the piston 107 arepreferably made from low carbon, high permeability steel, although othermagnetically permeable materials can be used. The slots 109 arepreferably evenly spaced around the circumference of the housing 103 sothat axial-periodic symmetry is maintained. The pair of coils 115 ispreferably wired such that they produce magnetic fields in oppositedirections. This configuration allows the magnetic field produced byeach coil 115 to add rather than cancel in an area between the coils115.

The configuration of the slots in the housing of the damper can bevaried to tune the flexibility of a housing. FIGS. 3A and 3B illustratea housing 127 that includes fewer longitudinal slots 109, and thereforehas less flexibility than a comparable housing having a larger number ofslots. Longitudinal slots 109 may also be carried through to an open end129 of a housing 131 as shown in FIGS. 4A and 4B. Slots 109 carriedthrough to the end 129 create a flexible housing 131 which promotes fullcontact between the housing 131 and the piston when the magnetic fieldis applied. Such a slot configuration may be particularly useful whenthe housing 131 is made from a thick-wall tubing. Greater housingflexibility can also be obtained by connecting pairs of slots 109 in ahousing 133 with a cross-slot 135 to form flexible fingers 137 havingfree ends 138 as shown in FIGS. 5A and 5B.

Depending on the thickness of the housing material and its consequentability to carry magnetic flux (permeability), and also on the magnitudeof the desired damping force, the number of coils 115 can vary from theembodiment shown in FIGS. 1 and 2. For example, a single-coil embodiment139 is shown in FIG. 6 and a 4-coil embodiment 141 is shown in FIG. 7.Except for the number of coils 115, and a solid core 143 rather than thehollow core described above, the embodiments shown in FIGS. 6 and 7 areidentical to the embodiment shown in FIGS. 1 and 2. More coils 115 arepreferable when the thickness of the housing is small in order to avoidmagnetic saturation of the housing. Magnetic saturation refers to themaximum amount of magnetization a material can attain, as will bereadily appreciated by one of ordinary skill in the art. The thicknessof the housing limits the amount of magnetization that can be induced inthe portion of the housing adjacent to the coils.

In some applications of the invention it is desirable to have themagnetic field, and therefore the damping force, applied most of thetime with only short instances of turning the damping off. This can beaccomplished by adding one or more permanent magnets to the system. Apermanent magnet can be used in the damper so that the damper is in itson-state and the housing pressing against the piston when no current isapplied to the electromagnetic coil. The electromagnetic coil serves tocancel the field of the permanent magnet as current is applied toprogressively turn the damper off.

A seventh exemplary embodiment of the motion control device of thepresent invention is illustrated in FIG. 8. As seen in FIG. 8, twoaxially polarized (i.e., the opposite faces of the disks are theopposite poles of the magnets) disk magnets 143 are positioned andoriented to bias a damper 145 into an on-state, i.e., a condition inwhich the housing is magnetically attracted to the piston. Amagnetically active portion 147 of a piston 149 includes three corepieces 151 between which the disk magnets 143 are located. The diskmagnets 143 are located immediately radially inward of the coils 115.The disk magnets 143 pull the housing 103 and the piston 149 together.In order to turn the damping off, the magnetic fields produced by thepermanent disk magnets 143 are at least in part, and preferablycompletely canceled by applying current to the pair of coils 115, whicheach generate magnetic fields that oppose those of the permanent magnets143.

An eighth exemplary embodiment of the motion control device of thepresent invention is illustrated in FIG. 9. In this case theelectromagnets do not cancel the magnetic field in all directions.Rather, the electromagnets cause the field of the permanent magnet to beredirected to a different path.

Like the embodiment shown in FIG. 8, the embodiment of a damper 150according to the present invention shown in FIG. 9 includes the housing103 having the same structure as that shown in FIGS. 1 and 2. Accordingto the embodiment shown in FIG. 9, a magnetically active portion 152 ofa piston 153 includes axially-polarized permanent ring magnets 155located immediately radially inward of the coils 115. The coils and ringmagnets are located between magnetically permeable core pieces 157 so asto define non-magnetic gaps 159 in the center of each ring magnet 155.Gaps 159 are less magnetically permeable than core pieces 157, andtherefore cause less magnetic flux through the center of themagnetically active portion 152. The core pieces 157 and ring magnets155 are held together by a non-magnetic connector 161. The connector 161is non-magnetic to prevent the generated magnetic field from beingshunted away from the interface between the housing 103 and themagnetically active portion 152. Alternatively, the core pieces 157 canbe held together by an adhesive. Any suitable adhesive can be used,including but not limited to epoxys and cyanoacrylates.

As is schematically shown in FIG. 10A, the non-magnetic gaps 159 at thecenter of the ring magnets 155 allow very little magnetic flux to followflanking paths through the non-magnetic gaps 159 at the center of thering magnets 155. As a result, a magnetic field 162 through the housing103 has a much lower reluctance (resistance to carrying a magneticfield) than the flux path through the center of each of the ring magnets155 and therefore radially draws the housing 103 and the piston 149together, as described above. In order to reduce the damping force,current is applied to the electromagnetic coils 115 which produce amagnetic field 163, as schematically shown in FIG. 10B. The current canbe adjusted such that the magnitude of the field produced by the coilsis equal to, but opposite, that of the ring magnets 155 where the fieldpaths cross into the housing 103. The magnetic field 163 adds to thatproduced by the ring magnets 155 to yield a net magnetic field 165 shownin FIG. 10C. That is, the magnetic field of each of the permanent ringmagnets 155 is redirected to flow through the high reluctance paththrough the open center of the ring magnets 155. The magnetic field atthe interface between the housing 103 and the piston that produces theattraction between the housing 103 and the piston 149 is canceled, andhence the damping force of the damper is reduced or entirely canceled.

A ninth exemplary embodiment of the motion control device of the presentinvention is illustrated in FIG. 11. As shown in FIG. 11, a spring 167can be added to an end of a damper according to the present invention toform a strut 169. The damper shown in FIG. 11 is identical in structureto that shown in FIGS. 1 and 2, except that the spring 167 is providedbetween the end 171 of the piston 107 and closed end 173 of the housing103. In a mechanical system the strut 169 provides the desired springstiffness in addition to a controllable level of damping force. Inaddition, as schematically shown in FIG. 11, a mechanical stop 175 isadded to the end of the housing 103 to hold the piston 107 in thehousing 103 and allow the spring 167 to be preloaded. The mechanicalstop 175 can optionally be included with damper embodiments as well.

Measured performance of a damper constructed according to the presentinvention is shown in the graph comprising FIG. 12. For purposes ofplotting the performance graph, the damper housing was constructed fromlow-carbon steel tubing having a 1.125 inch (28.58 mm) outer diameterand 1.000 inch (25.40 mm) inner diameter. The steel part of the housingwas 5.0 inches (127 mm) long. Four lengthwise slits each approximately0.040 inches (1 mm) wide 4.25 inches (108 mm) long were formed in thehousing. The piston included two coils wound onto a low carbon steeldouble bobbin having an overall length of 1.0 inches (25.4 mm). Thediameter of the steel poles of the piston was 0.990 inches (25.15 mm).The axial length of the two outer pole sections were each 0.145 inches(3.68 mm). The center pole section was 0.290 inches (7.37 mm) long. Thediameter of the solid center core of the piston was 0.689 inches (17.5mm). The two coils were each wound with 350 turns of 35 AWG magnet wireand were connected in series. The total resistance of the two coils wasapproximately 48 ohms. The total usable stroke of the damper was about 3inches (76 mm).

Turning now to the graph, initially, at low current, the example damperdisplays a proportionate, nearly linear behavior which then rolls off asmagnetic saturation effects begin to dominate as can be seen in FIG. 12.The damping force that is produced is almost perfectly coulombic withlittle or no velocity dependence. That is, the damping force is almostdirectly dependent on the current supplied to the coils. The data shownare peak forces obtained with the damper undergoing sinusoidalexcitation with a ±0.5 inches (12.7 mm) amplitude and a peak speed of 4inches/sec (102 mm/s). A curve obtained with a peak speed of 1 inch/sec(25.4 mm/sec) appeared to be nearly identical.

Although axial motion of the piston relative to the housing is what hasbeen discussed thus far, a damper according to the present inventionwill also function as a rotary damper with the piston rotating relativeto the housing.

A tenth exemplary embodiment of the motion control device of the presentinvention is illustrated in FIGS. 13 and 14. FIG. 13 shows an assembledexample of a rotational embodiment according to the present invention,with portions broken away to show some interior elements. FIG. 14 showsthe embodiment shown in FIG. 13 partially disassembled. In thisembodiment a coil 177 wound around a center steel bobbin 179 form astator 181. The stator 181 is positioned within a cavity defined by, andfor rotation relative to, a slotted housing 183. Slots 185 are connectedby cross-slots 186 to define fingers 187, which impart a high degree offlexibility to the housing 183. The highly flexible housing 183 allowsmaximum contact between the stator 181 and the housing 183 when themagnetic field is energized. Bearings 188 are included in the stator 181to support a shaft 190 with which the housing 183 rotates.

A damper according to the present invention generates strong coulombicpressing forces when the outer surface of the magnetically activeportion of the piston or stator makes direct contact with the innersurface of the steel housing. In fact, the inventor herein has foundthat damper performance actually improves after being initially operateddue to an apparent “wearing-in” process. During the wearing-in processfriction between the surfaces of the housing and the piston causes somewear to occur which effectively laps or burnishes the contactingsurfaces such that “high spots” (large surface features) are removed andthe housing and piston (or stator) contact more intimately. Thisimproves the efficiency of the magnetic circuit and increases totalcontact surface area so that the overall damping force is increased.

In some applications of the present invention, it is desirable to placea layer of damping material or acoustic foam 189 around the outside ofthe housing as seen on the exemplary damper shown in FIG. 15. Thecomponents of the damper shown in FIG. 15 are identical to the exemplarydampers discussed with respect to FIGS. 1–14. Such an acousticallyinsulating material will serve to attenuate any high frequencysqueaking, rubbing or clanking sounds that may occur due to a metalhousing moving against a metal piston. The desirability of such addedacoustic material depends on a number of factors, including: the actualthickness of the housing; the resonant characteristics of the housing;the looseness of the fit between the housing and the piston, thealignment of the parts during application of the damper; and thepresence of elastomeric bushings in the clevis eyes used to mount thedamper. Lubricant (grease or oil) can also be added so that the parts ofthe damper slide smoothly relative to each other in the off-state.Suitable acoustic material will be readily apparent to one of ordinaryskill in the art.

A similar quieting effect can be achieved by adding an intermediaryfriction increasing layer to the rubbing surfaces of the piston orstator, or the inner surfaces of the housing. Examples of such materialsmay be a thin polymeric layer such as polyethylene or nylon, or acomposite friction material such as that typically used in vehicleclutches and brakes. Such a friction layer eliminates metal to metalcontact and reduces long term wear. However, the presence of such layerof friction material will in general make the magnetic circuit lessefficient. Unless the friction material has a high permeability like lowcarbon steel it increases the reluctance of the magnetic circuitdramatically and lowers the amount of damping force when the damper isin the on-state.

According to yet another embodiment of the present invention, amagnetically controlled damper can further include an integratedposition sensor. Exemplary embodiments of a damper including a positionsensor according to the present invention are shown in FIGS. 16–23.Preferably, a magnetic friction damper 191 includes sensor 193, such asa linear potentiometer, including a first portion 194 and a slider 196.The first portion is attached to the housing 103 by brackets 198. Theslider 196 is coupled to the damper piston 195 by a small engagement pin197 that passes through one of a plurality of slots 109 in the housing103 of the magnetic friction damper 191.

A eleventh exemplary embodiment of the motion control device of thepresent invention is illustrated in FIGS. 16–18. FIGS. 16–18 show adamper similar to the damper shown in FIGS. 1 and 2. Otherwise identicalto the piston shown in FIGS. 1 and 2, the piston 195 includes acircumferential groove 199 between electromagnetic coils 115. The sensor193 is mounted along the side of the damper housing with brackets 198such that an extension, such as the pin 197 of the slider 196 on thepotentiometer 193, can pass through one of the longitudinal slots 109 inthe damper housing 103. The groove 199 in the damper piston 195 acceptsthe pin 197 and causes the slider 196 to move longitudinally in concertwith the piston 195 while permitting relative rotational movementbetween the piston and the housing. Thus, for example, electricalresistance of a potentiometer varies in proportion to the pistondisplacement in the housing, thereby indicating the relative position ofthe housing 103 and the piston 195.

Alternatively or in addition to measuring linear displacement with thesensor 193, the sensor can be used to measure the relative velocity oracceleration of the housing 103 and the piston 195. Furthermore, sensor193 can be a velocity sensor or an accelerometer, which are readilycommercially available and with which one of ordinary skill in the artis well acquainted. A device for interpreting the signal from sensor193, such as a general purpose computer 200 having a memory 201, is inelectrical communication with electrical connections 202 on the sensor193. Computer 200 can further be provided with logic in the memory 201which can determine relative position, velocity, or acceleration basedon the electrical signals sent by the sensor 193, and can store datarepresentative of one or more of these parameters. Because one ofordinary skill in the art readily appreciates the details of the use ofsuch a computer 200 and logic usable with sensor 193, further detailswill not be provided herein.

A circumferential groove 199 rather than a hole in the piston 195 ispreferred because the circumferential groove 199 does not inhibitrotational motion of the piston 195. Allowing free rotational motion ofthe piston 195 relative to the housing 103 is important so that theclevis eyes 121 at the ends of the damper 191, when provided, can beeasily properly aligned with the mounting pins in the components towhich the damper 191 is attached so that the damper 191 does not bindduring use.

Twelfth, thirteenth and fourteenth exemplary embodiments of the motioncontrol device are illustrated in FIGS. 19, 20 and 21 respectively. Asseen in FIGS. 19–21, a circumferential groove can be located on otherparts of the piston 195 as well. For example, as seen in the embodimentshown in FIG. 19, a groove 203 is formed into the shaft of the piston195 just behind a magnetically active portion 205 of the piston. In theembodiment shown in FIG. 20, a groove 207 is formed between a lip 209formed into the piston 195 and a rear end 211 of the magnetically activeportion 205 of the piston 195. In the embodiment shown in FIG. 21, adisk-shaped member 213 is attached to a free end 215 of the piston 195to define a groove 217. Other than the arrangement of thecircumferential groove the embodiments shown in FIGS. 19–21 areidentical to the embodiment shown in FIGS. 16–18.

An experimental example of a damper including a position sensor wastested by the inventor herein. The prototype utilized a Panasonicpotentiometer (part number EVA-JQLR15B14, Matsushita Electric (PanasonicU.S.A.), New York, N.Y., U.S. distributers include DigiKey and NewarkElectronics) with a working stroke of 3.94 inches (100 mm). Electricalresistance varied linearly from 0 to 10 Kohms. The potentiometer wasmounted to the damper housing using hot-melt adhesive. The originalrectangular extension on the slider was modified into the form of asmall diameter pin to fit through one of the longitudinal slots in themagnetic friction damper housing. In the example, the groove in thepiston was made by adding a small, spaced plastic disk to the end of anexisting piston as shown in FIG. 21. The final result was an integratedvariable resistance sensor whose output varied linearly with theposition of the damper piston. Further, the pin and groove geometryallowed free rotational motion of the piston within the housing, afeature that allowed for proper alignment of the clevis eyes duringdamper installation and use.

A fifteenth exemplary embodiment of the motion control device of thepresent invention is illustrated in FIGS. 22 and 23. Another exemplaryembodiment of a damper including a position sensor is shown if FIGS. 22and 23. In this embodiment a rotary sensor 219 (e.g., a rotarypotentiometer) is used in the position sensor. Alternatively, a rotaryoptical encoder can be used in the position sensor. The rotary sensor219 is mounted to the housing by a bracket 220 and is coupled to themotion of a piston 221 by means of the integrated rack and pinion system223. A pinion gear 225 is coupled to the rotary sensor 219 (or opticalencoder) by an axle 227. The piston 221 includes a shaft 228 that ismolded (of, e.g., plastic) or otherwise formed to include a rack 229. Itis preferable to allow relative rotation between the piston and thepinion gear. Therefore, it is preferable that the rack 229 is formedaround the entire circumference of the piston 221.

In addition to the variable resistance sensors discussed above, othersensing devices may alternatively be used, including variable inductanceor variable capacitance sensors, optical encoders, flex or bend sensorsetc. and are all within the spirit and scope of the present invention.As discussed in reference to FIGS. 16–23 a sensor can be used to measurerelative velocity or acceleration as well as relative position between apiston and a housing.

Further, although the magnetic damper including a position sensor hasbeen described in the context of collet type dampers, the same positionsensors may be included with MR or ER dampers. Examples of such MR or ERdampers are described in U.S. Pat. Nos. 5,284,330, 5,277,281 and5,018,606, which are herein incorporated by reference in theirentireties.

Magnetically actuated motion control devices according to the presentinvention, including those described herein, are useful in manyapplications. FIGS. 24–32 illustrate a number of exemplary applicationsfor the present invention device. For example, FIG. 24 shows the use ofmagnetically controllable dampers according to the present invention 230in a washing machine 231. Magnetically controllable friction dampers canprovide a high level of damping when the washing machine 231 passesduring a resonance cycle and can be turned off during high speed spin toprovide optimum isolation of the spinning basket or drum 232.

FIG. 25 shows several possible uses of the present invention in anautomobile, truck, or other vehicle. Magnetically actuated motioncontrol devices according to the present invention can be used as asemi-active seat suspension when located between a seat 233 and anassociated base 235. Dampers according to the present invention can alsobe used as a locking element 237 in a steering column 239 including tiltand telescope mechanisms 241, 243. A magnetically actuated motioncontrol device 230 in its on-state locks the steering column 239 inplace. In its off-state, the damper allows the steering wheel to tiltand telescope into a desired position. Other applications in motorvehicles include the use of a damper as an interlock mechanism ingearshift mechanisms (not illustrated).

Another application for the invention is as a locking member 245 forvarious types of furniture such as office chairs, for example. FIG. 26Aillustrates the use of a magnetically actuated motion control device 230in a height adjustor 245 of an office chair 247. FIG. 26B illustratesthe use of a magnetically actuated motion control device 230 as alocking mechanism 249 for the back tilt motion of the chair 247 and as alocking mechanism 250 for a height adjustable armrest 252 of the chair247, and which can be connected between the armrest 252 and either aseat 254 or a backrest 256 of the chair 247. An electrical control 251is used by an operator to selectively turn off the magnetically actuatedmotion control device 230, thereby allowing the chair 247 to tilt.

FIG. 27 illustrates the use of magnetically actuated motion controldevice 230 as a locking mechanism 253 for an adjustable height table255. The adjustable height table 255 also includes a control 258 wiredto the locking mechanism 253. The control 258 selectively allowsselective locking of the adjustable table 255 by alternatively turningthe dampers on and off.

FIGS. 28A and 28B show a magnetically actuated motion control device 230according to the present invention used as a locking mechanism for atilting work surface 257 into position (FIG. 28B) or for locking aflipper door 259 into place (FIG. 28A).

Another area of application for the motion control device of the presentinvention is the area of haptics, where a linear or rotary embodiment ofthe invention may be used to provide tactile force feedback to anoperator. FIG. 29 illustrates a force—feedback steering wheel 261 thatuses a rotary damper 263, such as that described in reference to FIGS.13 and 14. Such a device can also be used in “steer-by-wire” mechanismson vehicles such as cars, trucks or industrial jitneys and forklifts.The present invention can also be used in computer games as aforce-feedback steering wheel that is responsive to virtual action in agame. In the example shown in FIG. 29, the damper 263 is coupled to arotary position sensor 265 so that the damping can be coupled to theposition of the steering wheel.

The present invention can also be used as a small controllable frictionbrake inside computer pointing devices, such as a computer mouse 267 asshown in FIG. 30. The mouse 267 includes a mouse ball 269 that is inrolling contact with a y-drive pinion 271 and an x-drive pinion 273. Thedrive pinions 271, 273 are each respectively coupled to a y-encoderwheel 275 and a x-encoder wheel 277 with a rotary brake 279 of the typedescribed in reference to FIGS. 13 and 14, for example. Each encoderwheel 275, 277 is positioned so as to rotate through an encoder sensor280. The rotation of an encoder wheel is sensed by a respective encoderwhich sends an electrical signal representing the movement of the mouseball 273 in an x-y plane which passes through pinions 271, 273.

The invention can also be used to provide an active force feedbacksteering wheel 281 as shown in FIG. 31. In this application a pair ofclutches 283, 285, similar in structure to the rotary damper describedwith reference to FIGS. 13 and 14, are used to selectively couple thesteering wheel 281 to either clockwise or counter-clockwise rotatinghousings 287, 289. In a clutch arrangement, the stator and the housingare each rotatable, and are rotatable relative to one another. A motor291 is coupled to clockwise and counter-clockwise housings 287, 289 by apinion drive 293. A shaft 295 extending from the steering wheel passesthrough the housing 289 and is coupled to stators 297, 299 of theclutches 283, 285, respectively. The shaft 295 can include bearings orother similar structures where the shaft passes through the housings287, 289, to permit relative rotational movement between the shaft andthe housings. A rotary position sensor 298 is coupled to the end ofshaft 295 to detect the rotation of the steering wheel 281. The stators297, 299, provide friction damping in the clockwise andcounter-clockwise directions as in the manner described with referenceto FIGS. 13 and 14 with contact surfaces 301, 303. Thus, the steeringwheel 281 can actually be forced to turn with a prescribed amount offorce in either direction with the ultimate driving source being asimple single direction motor 291.

The invention can also be used in flexible fixturing systems such as thefixturing system 305, schematically illustrated in FIG. 32. In thisexample, an array of struts 307, like those described in reference toFIG. 11, are each coupled to extensions 309 and are used to hold anirregularly shaped object 311 in position for machining or gauging ofthe object 311. Each of the struts 307 can selectively lock or releasean extension 309 so that objects of various sizes and shapes can beaccommodated and held in place.

In addition to the embodiments of the present invention shown in FIGS.1–23 and described hereinabove, other embodiments of the presentinvention shown in FIGS. 33–43 can be interchanged for the exemplarymagnetically actuated control devices illustrated in the applicationsdescribed with reference to FIGS. 24–32.

The sixteenth preferred embodiment of the motion control device isillustrated in FIG. 33. As seen in FIG. 33, the motion control device iscomprised of a damper 313 that includes a housing 103 having slots 109and a piston 315 having a magnetically active portion 317 that includesa permanent disk magnet 319 sandwiched between core pieces 321. The corepieces 321 are held together by the magnetic field generated by thepermanent magnet 319, eliminating the need for connectors or adhesivesin the magnetically active portion of the piston 315. Thus, the assemblyof the damper 313 is greatly simplified. Because the magnetic fieldgenerated by the permanent magnet 319 cannot be varied, the damper 313is always in an on-state. That is, the housing 103 always squeezes thepiston 315 with the same force.

Seventeenth and eighteenth exemplary embodiments of the motion controldevice of the present invention are illustrated in FIGS. 34 and 35.However, as seen in FIGS. 34 and 35, the squeezing force between thehousing and the magnetically active portion of the piston can be variedby introducing a variable width gap into the magnetically active portionof the damper. As seen in FIG. 34, a damper 323 of this type includes ahousing 103 including a plurality of slots 109, within which a hollowpiston 325 is located. A magnetically active portion 326 of the piston325 includes an end 327 connected to a control rod 329. The end 327includes an axially polarized disk magnet 330 that is sandwiched betweena cap piece 332 and a first pole piece 331. The control rod 329 isattached to the cap piece 332.

According to an exemplary embodiment shown in FIG. 34, a second polepiece 333 is attached to the hollow piston 325. A clearance 335 betweenthe control rod 329 and the second pole piece 333 allows the second polepiece 333 to slide relative to the control rod 329. A lever 337 locatedon the outer surface of the piston 325 is connected to the control rod329 through an opening 338 in the piston 325 so that as the lever 337 isturned, the control rod 329 pushes the end 327 of the magneticallyactive portion 326 toward or away from the second pole piece 333attached to the hollow piston 325. In this way, an air gap 339 ofvariable size is introduced into the magnetically active portion 326.The gap 339 increases the reluctance within the magnetically activeportion 326, thereby diminishing both the force with which the housing103 squeezes the piston 325, and also the frictional damping forceproduced by the damper.

Alternatively, as seen in FIG. 35, a damper 341 according to the presentinvention can include a control rod 343 having a threaded end 345 thatthreads into a tapped second pole piece 347 that is attached to thehollow piston 325. Like the embodiment shown in FIG. 34, the control rod343 is attached (at the threaded end 345) to a cap piece 349 thatsandwiches an axially polarized disk magnet 350 with a first pole piece351. The control rod 343 is connected to a knob 353 that is exposedthrough an opening 355 in the hollow piston 325. Rotating the knob 353rotates the control rod 343 and causes the tapped second pole piece 347to move relative to the cap piece 349. In this way, a variable air gap357 is introduced into the magnetically active portion. As discussed inreference to the embodiment shown in FIG. 34, the variable gap 357 canbe used to control (diminish) the damping force produced by the damper.

Nineteenth and twentieth exemplary embodiments of the motion controldevice of the present invention are illustrated by FIGS. 36A–37B, and38A–38B respectively. As seen in FIGS. 36A–38B, according to the presentinvention the components of a magnetically actuated motion controldevice can be reversed with respect to the other exemplary embodimentsdiscussed thus far. For example, as seen in FIGS. 36A and 36B, a damper359 includes a housing 361 that defines a cavity 363 in which a piston365 is located. The piston 365 includes four slots 367 that extend froman open end 369 of the piston 365. Although the piston 365 is tubular, apiston can have any suitable cross-sectional area such as square,cylindrical etc. A magnetic field generator, such as coils 371 (shownschematically), is located in a magnetically permeable assembly 373having pole pieces 375. At least a portion of the slotted piston 365 ismagnetically permeable so that when a magnetic field is generated by thecoils 371, the piston flexes and presses outward against the pole pieces375 of the magnetic assembly 371 located on the housing 361.Accordingly, the friction damping force can be controlled by controllingthe magnetic field generated by the coils 371.

As seen in FIGS. 37A and 37B, the piston 365 is hollow. A hollow pistonis preferred because a hollow piston can easily flex outward in responseto an applied magnetic field. However, according to an embodiment shownin FIGS. 38A and 38B, a piston 377 can be solid. Slots 379 extendthrough the solid piston 377 to define bands, sections, tabs, or fingers381. The fingers 381 flex outward in response to an applied magneticfield to produce a frictional damping force. An advantage of having asolid piston is that magnetic saturation of the piston can be mitigated.

Other embodiments of a magnetically actuated motion control deviceaccording to the present invention include bearing components thatcontact the components of the magnetically controlled motion controldevice, e.g., a housing and a piston, and provide smooth relative motionbetween the components when the motion control device is in itsoff-state.

For example, a twenty-first exemplary embodiment of the motion controldevice of the present invention is illustrated in FIGS. 21 and 39–41C. Amagnetically actuated motion control device 383 includes a piston 385which fits within a housing 387. The piston 385 includes one or morelongitudinal slots 388 which extend through an end 389 of the piston 385to define one or more fingers 390. The housing 387 includes magneticfield generators, such as coils 391, mounted between pole pieces 393.The housing 387 defines a cavity 395 connecting opposing open ends 397,399 of the housing 387. In this way, the piston 385 can pass throughboth open ends 397, 399 of the housing 387 during its stroke.Accordingly, the axial length of the housing 387 can be much shorterthan the axial length of the piston 385, thereby providing a compactdevice. Trunnion mounts 401, which extend from the housing 387, allowthe open ended housing 387 to be mounted to a separate device.

Turning to a partial view 39A, a bearing assembly 403 is locatedradially inward of each of the coils 391 and within radial grooves 404defined by the pole pieces 393 of the housing 387. Each bearing assembly403 includes an annular spring 405 (see also, FIG. 41B) located betweena coil 391 and an expandable bearing 407. Preferably, the spring is aband of compliant, elastomeric material, e.g., a sponge material or anO-ring.

The expandable bearing 407 contacts the surface of the piston 385 and isbiased by the spring 405 radially inward toward the outer surface of thepiston 385. As a result, a small gap 409 is maintained between thehousing 387 and the piston 385 when the coils 391 are not energized.Preferably, the radial thickness of each bearing 407 is greater than thethickness of the gap 409 so that the bearing remains captured within therespective radial groove 404. Preferably, only the bearings 407 contactthe outer surface of the piston 385 when the magnetically actuatedmotion control device is in its off-state. By spacing a plurality ofbearings 407 axially along the housing 387, the piston 385 and thehousing 387 are prevented from binding, or moving out of axial alignmentrelative to one another (also referred to as “cocking”) when the deviceis in an off-state.

Energizing the coils 391 causes the fingers 390 to flex in a radiallyoutward direction and press against the inner surface of the housing387. At the same time, each bearing 407 is pressed outward by thefingers 390, thereby compressing the spring 405. Thus, when the motioncontrol device 383 is in its on-state, the gap 409 between the housing387 and the piston 385 is eliminated as seen in FIGS. 40, 40A and 41A asthe magnetic field generated by the coils 391 causes the housing 387 andthe piston 385 to press firmly against one another.

In order to provide firm contact between the housing 387 and the piston385, the bearing 407 must expand radially as the fingers 390 flex towardthe housing 387 in response to a magnetic field generated by the coils391. As seen in FIG. 41C, one embodiment of the annular bearing includesa split 411 to allow for radial expansion. Optionally, split 411 can beeliminated by forming bearing 407 of a material flexible enough topermit its radial expansion. Preferably, the bearing is made from astrip of flexible, low friction material. Examples of suitable bearingmaterials include nylon materials, e.g., molybdenum disulfide fillednylon fibers, Hydlar HF (A.C. Hyde Company, Grenloch, N.J.), which is amaterial including nylon reinforced with Kevlar fibers,polytetrafluorethylene materials, e.g., Teflon®, Derlin AF® (E.I. DupontNemours and Co., Wilmington, Del.), which is teflon filled with anacetal homopolymer, and Rulon® (Dixon Industries, Bristol, R.I.), whichis a material including Teflon® reinforced Kevlar® fibers, Vespel® (E.I.Dupont Nemours and Co., Wilmington, Del.), which is a polyimidematerial, Ryton® (Philips Petroleum Co., Battlesville, Okla.), which isa material including polyphenylene sulfide filled with carbon fiber, orbrass. The preceding list is not exhaustive, and other suitablematerials will be apparent to one with ordinary skill in the art.

As explained earlier, the magnetic field generators, e.g., coils can bemounted to either the housing or the piston with the other of thehousing or the piston being split into one or more flexible fingers.FIG. 42 shows a twenty-second embodiment of the present inventionincluding a piston 413 having two magnetic coils 391 located within acore 414 and a slotted housing 415 in which the piston 413 is located.Like the embodiments discussed in reference to FIGS. 1 and 2, thehousing 415 includes one or more longitudinal slots 417 that define oneor more flexible fingers 419.

The piston 413 slides within the housing 415 on bearing assemblies 421,which are each located radially inward of the coils 391 and bear againstthe inner surface of the housing 415. Each bearing assembly includes anannular spring 425, which is located between an annular bearing 427 andone of the respective coils 391. The spring 425 biases the bearing 427radially outward and away from the magnetically active portion of thepiston to create a gap 428 between the outer surface of the piston 413and the inner surface of the housing 415. Preferably, each bearing 427and spring 425 are of the same structures and materials as thosediscussed in reference to FIGS. 39–41.

According to a twenty-third exemplary embodiment shown in FIG. 43,bearing assemblies are located axially spaced from coils 391. In thisembodiment a piston 429 is located within a housing 430 having structuresuch as that described in reference to FIG. 42, including slots 432defining one or more fingers 434. The piston 429 includes a main body431 having a shoulder 433 at one end, an end cap 435 including ashoulder 436 that opposes the shoulder 433 and two steel cores 437sandwiched between the end cap 435 and the main body 431.

A first bearing assembly 439 is located between the cores 437 and theshoulder 433 in the cores 437. A second bearing assembly 441 is locatedbetween the shoulder 436 and the main body 431. Each bearing includes aspring 438 that biases a bearing 440 against the inner surface of thehousing 430. Preferably, the spring 438 and bearing 440 are constructedin the same manner as described with respect to the previousembodiments. The bearings 440 are biased against the inner surface ofthe housing 430 to create a gap 442 between the cores 437 and the innersurface of the housing 430 when the coils are not energized, i.e., themagnetically actuated motion control device is in an off-state.

The cores 437 are secured to the main body of the piston 429 by aninterference fit between the outer surface of the cores 437 and theinner surface of the piston 429. The cores 437 and end cap 435 aresecured to one another by a bolt 443 and a nut 445. The bolt 443 passesthrough aligned bores in the cores 437 and the end cap 435. Accordingly,as exemplified by this embodiment, the bearing assemblies need not belocated between the magnetic field generator (e.g., coils 391) and theopposing slotted member.

While two magnetic field generators, e.g., coils 391, are illustrated inFIGS. 39–42, one of ordinary skill in the art will readily appreciatethat one, or three or more, magnetic field generators may alternativelybe used within the spirit and scope of the invention. Similarly,although two bearing assemblies are illustrated in FIGS. 39–42 one ormore bearing assemblies may be used within the spirit and scope of theinvention.

Advantages of using bearing assemblies in a magnetically actuated motioncontrol device in order to create a gap between the housing and thepiston include maintaining the piston and the housing in axial alignmentand creating smooth, fluid-like, relative movement between the housingand the piston while the damper is in its off-state.

An example of a situation in which it may be important to provide smoothmovement between the housing and the piston is when an embodiment of thepresent invention is used as a locking mechanism in a hinged vehicledoor. In the example shown in FIG. 44, a car 447 includes a body 449 anda door 451 that swings on a hinge 453 relative to the body 449. Thehousing 387 of a motion control device 383 (shown in FIGS. 40–41C) ismounted in the door 451 of the car 447. Because the door 451 has limitedspace in which to fit extra components, the housing 387 is preferablyshort relative to the length of the piston 385. The slotted piston 385is attached at one end to the body of the car. As the door is swung openand closed, the piston 385 moves within the housing 387. An operator canlock the door 451 into any position by activating a switch 455 whichenergizes the magnetic field generator to cause the piston and thehousing to press against one another together, thus holding the door inposition.

The present invention has been described with reference to exemplaryembodiments. However, it will be readily apparent to those skilled inthe art that it is possible to embody the invention in specific formsother than as described above without departing from the spirit of theinvention. The exemplary embodiments are illustrative and should not beconsidered restrictive in any way. The scope of the invention is givenby the appended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

1. A dynamic state sensing movable member magnetically actuated motioncontrol device, the magnetically actuated motion control deviceincluding a housing, said housing defining a cavity for receiving amovable member, said housing comprised of a magnetic field attractedmaterial, said movable member-located in said cavity, said movablemember movable in said cavity relative to said housing, anelectromagnetic coil, said electromagnetic coil generating a magneticfield to draw said housing magnetic field attracted material in towardsand into contact with said movable member when supplied with a currentto control motion of said movable member relative to said housing, asensor comprising a first sensor member secured to the housing a secondsensor member coupled to the movable member, wherein a relative positionbetween the first sensor member and the second sensor member indicatesthe position of the movable member relative to the housing.
 2. A deviceas claimed in claim 1 wherein said magnetic field attracted material iscomprised of a steel.
 3. A device as claimed in claim 1 wherein saidmagnetic field attracted material is comprised of an iron alloy.
 4. Adevice as claimed in claim 1 wherein said housing comprises a slottedhousing.
 5. A device as claimed in claim 1 wherein said sensor comprisesa potentiometer.
 6. A device as claimed in claim 1 wherein said sensorcomprises a velocity sensor.
 7. A device as claimed in claim 1 whereinsaid sensor comprises an accelerometer.
 8. A device as claimed in claim1 including a computer in electrical communication with the sensor.
 9. Adevice as claimed in claim 1 wherein said movable member comprises apiston.
 10. A device as claimed in claim 1 wherein said housingcomprises a slotted tube.
 11. A dynamic state sensing movable membermagnetically actuated motion control device, the magnetically actuatedmotion control device including a flexible piston housing, said flexiblepiston housing defining a cavity for receiving a movable piston, saidflexible piston housing comprised of a magnetic field attractedmaterial, said movable piston located inside said flexible pistonhousing cavity, said movable piston movable in said flexible pistonhousing cavity relative to said flexible piston housing along a lengthof said flexible piston housing, an electromagnetic coil, saidelectromagnetic coil generating a magnetic field to draw said flexiblepiston housing magnetic field attracted material inward towards saidmovable piston when supplied with a current with contact of said movablepiston and said drawn inward flexible piston housing controlling motionof said movable piston along the length of said flexible piston housing,and a sensor comprising a first sensor member secured to the flexiblepiston housing, a second sensor member coupled to the movable piston,wherein a relative position between the first sensor member and thesecond sensor member indicates the position of the movable piston alongthe length of the flexible piston housing.
 12. A dynamic state sensingmovable member magnetically actuated motion control device, themagnetically actuated motion control device including a flexible pistonhousing, said flexible piston housing defining a cavity for receiving amovable member piston, said flexible piston housing comprised of amagnetic field attracted material, said movable member piston locatedinside said flexible piston housing cavity, said movable member pistonmovable in said flexible piston housing cavity relative to said flexiblepiston housing along a length of said flexible piston housing, anelectromagnetic coil, said electromagnetic coil generating a magneticfield to draw said flexible piston housing magnetic field attractedmaterial inward towards said movable member piston when supplied with acurrent with a contact of said movable piston and said drawn inwardflexible piston housing controlling motion of said movable member pistonalong the length of said flexible piston housing, and a movable memberpiston sensor wherein said movable member piston sensor senses aposition of said movable member piston relative to said flexible pistonhousing.